The head of the United Nations nuclear agency has arrived in Iran, hoping to open up a once-secret nuclear facility to inspectors.

Hours before International Atomic Energy Agency chief Mohamed ElBaradei landed in Tehran Saturday, Iran's president launched another defense of his country's actions.

President Mahmoud Ahmadinejad said Iran never tried to hide the existence of a nuclear facility near the holy city of Qom, and he accused the United States of making a big mistake.

The U.S. and several allies contend Iran tried to keep the uranium enrichment facility a secret. ElBaradei said earlier that Iran "was on the wrong side of the law."

ElBaradei's visit comes two days after world powers demanded Iran give inspectors access to the facility. Iran has said it will comply with the demand.

Iran made the concession after meeting with diplomats from six world powers in Geneva on Thursday. Iranian officials say the visit by ElBaradei is not connected with the talks in Geneva.

Iranian officials say the meeting with ElBaradei will discuss a plan that calls for Tehran to ship some of its low-enriched uranium to Russia for reprocessing. The uranium would then be used to fuel a medical research reactor.

Russian Foreign Minister Sergei Lavrov said the Geneva talks "inspire cautious optimism." U.S. President Barack Obama said Iran must take concrete steps to prove its nuclear program is for peaceful purposes.

Diplomats from Russia, China, Britain, France, the United States and Germany took part in Thursday's meeting.